CS2000-OTP

DS758PP1

15

binary portion. In this configuration, the maximum multiplication factor is approximately 1,048,575 with a

resolution of 244 PPM.

The 20.12 format is enabled by the LFRatioCfg global parameter. The 20.12 ratio format is only available

when the device is running in Hybrid PLL Mode. In Auto Fractional-N Source Selection Mode (see section

5.4.6.2 on page 17) when CLK_IN is not present the LFRatioCfg parameter is ignored and the ratio format

is 12.20.

It is recommended that the 12.20 High-Resolution format be utilized whenever the desired ratio is less

than 4096 since the output frequency accuracy of the PLL is directly proportional to the accuracy of the

5.4.3

Manual Ratio Modifier (R-Mod)

stored in the register space remain unchanged). The available options for R-Mod are summarized in

Table 2 on page 15. R-Mod is enabled via the M2 pin in conjunction with the appropriate setting of the

M2Config[2:0] global parameter (see Section 5.7.2 on page 20).

Table 2. Ratio Modifier

5.4.4

Automatic Ratio Modifier (Auto R-Mod) - Hybrid PLL Mode Only

The Automatic R-Modifier uses the CLK_IN Frequency Range Detector to implement a frequency depen-

tor determines the ratio between the frequency of the internal SysClk and the CLK_IN input signal. The

result of the ratio measurement is the internal status signal called FsDetect[1:0].

changed. The Automatic Ratio Modifier is enabled either by the AutoRMod modal parameter or via the

M2 pin in conjunction with the appropriate setting of the M2Config[2:0] global parameter (see Section

5.7.2 on page 20).

Table 3. Automatic Ratio Modifier

Referenced Control

Parameter Definition

LockClk[1:0] ..........................“Lock Clock Ratio (LockClk[1:0])” section on page 24

LFRatioCfg ............................“Low-Frequency Ratio Configuration (LFRatioCfg)” on page 26

FracNSrc ...............................“Fractional-N Source for Frequency Synthesizer (FracNSrc)” section on page 24

RModSel[1:0]

R Modifier

00

0.5

01

0.25

10

0.125

11

0.0625

Referenced Control

Parameter Definition

Ratio 0-3................................“Ratio 0 - 3” on page 24

RModSel[1:0] ........................“R-Mod Selection (RModSel[1:0])” section on page 23

M2Config[2:0]........................“M2 Pin Configuration (M2Config[2:0])” on page 26

FsDetect[1:0]

Auto R Modifier

00

> 224

1

01

96 - 224

0.5

10

< 96

0.25